Distinguishing telecined progressive video from normally interlaced video is significant for both video display and video encoding. If a high quality progressive display is intended, a good solution for a telecined progressive source of video is to correctly “weave” together pairs of associated fields for display as individual frames. In contrast, normally interlaced video is de-interlaced for display as a sequence of frames, a process that is not perfect and involves many tradeoffs. For compression, if the format of the video can be correctly discerned and the parity of progressive video identified (i.e., the correct association between a top field and a bottom field of a frame), then compression quality can be much higher by coding the video as natively progressive, instead of individually coding the interlaced fields (which must be done if the progressive format cannot be identified).
Conventional solutions for detecting interlaced fields originating from progressive frames use pixel differences and look for “combing” artifacts in the video. The pixel differences and combing artifacts can distinguish normally interlaced video from telecined progressive video. In addition, combing artifacts are found in frames formed from the two possible different woven combinations of fields (i.e., a top field with a next bottom field and the top field with a previous bottom field, respectively) to correctly identify the parity of a progressive video source.
The conventional solutions are easily fooled by vertical motion and/or by low motion. In such cases, the combing artifacts do not always appear in interlaced material. Therefore, the conventional solutions sometimes incorrectly identify an interlaced source as a progressive source and/or are unable to discern the correct parity of a progressive source in the absence of horizontal motion. In addition, the conventional solutions have difficulty with material having significant vertical details (i.e., high vertical frequency material), which are often incorrectly classified as combing artifacts, leading to false positives and negatives.